The following methods used to improve the optical purity of 1-benzyl-3-aminopyrrolidine are well known. For example, racemic 1-benzyl-3-aminopyrrolidine is optically resolved with an optically active carboxylic acid derivative (Japanese Unexamined Patent Application Publication No. 02-218664); an optically active amino acid derivative or an optically active tartaric acid derivative is used as an optical resolution agent (Japanese Unexamined Patent Application Publication Nos. 09-124595 and 09-176115); and an optically active camphorsulfonic acid is used as the optical resolution agent (Japanese Unexamined Patent Application Publication No. 09-216866). However, none of the above optical resolution agents are readily available and are inexpensive. Therefore, these methods are unsatisfactory for industrial production.
In terms of an alternative method, an optically active material is converted to a pyrrolidine derivative in order to produce optically active 1-benzyl-3-aminopyrrolidine. However, this compound is often racemized during the derivation process; therefore, it is difficult to produce high-optical-purity 1-benzyl-3-aminopyrrolidine (for example, Japanese Unexamined Patent Application Publication No. 2000-53642, PCT Japanese Translation Patent Publication No. 07-506110, etc.). Consequently, there is a demand for the development of a method to improve the optical purity of 1-benzyl-3-aminopyrrolidine produced by these methods.
In addition to the salt of 1-benzyl-3-aminopyrrolidine with an optically active acid described above, racemic 1-benzyl-3-aminopyrrolidine monohydrochloride (Tetrahedron Letters 42 (2001) 5,645), optically active 1-benzyl-3-aminopyrrolidine dihydrochloride (Japanese Unexamined Patent Application Publication No. 02-218664), and racemic 1-benzyl-3-aminopyrrolidine monofumarate are disclosed. However, no method has been reported to improve the optical purity of 1-benzyl-3-aminopyrrolidine by forming the salts thereof.
As described above, a method to improve the optical purity of 1-benzyl-3-aminopyrrolidine having a low optical purity using an inexpensive agent via a simple procedure is unknown.